Final Fantasy X Walkthrough
Blitzball: HP - Stamina

If players didn't have stamina, they could hog the ball all game without ever tiring. Instead, the person carrying the ball loses HP, or stamina, as they go. When they give up the ball they gain it back again. Shooting and passing both take HP too - it's marked right next to each command how much HP you use to do that thing. You can shoot or pass even if you don't have enough HP, but you don't do very well. It's better to try to shoot or pass before you get too low on HP.